Malware (or malicious software) is a computer program that is often designed to disrupt network communications, gain control over computers or networks, or secretly gather personal information about users. Malware typically includes viruses, trojans, adware, and spyware, to list a few examples.
Malware is created for a variety of reasons such as to achieve wide-spread notoriety or for personal gratification. Alternatively, malware is created to secretly access financial information such as banking records, credit card numbers, and/or social security numbers of individuals. While these exploits are frustrating and possibly destructive, they are also fairly simple.
Currently, signature based anti-malware software combats malware by using hashes (i.e., unique signatures of the malware) to identify and quarantine (or remove) the malware. Typically, the anti-malware software utilizes databases containing records of hashes for known malware. If a program's hash matches a hash of known malware, then the program is quarantined or removed.